Then recuring to the technical economy method and mathematic method, we set up an improved NPV model which includes more variables such as the increase rate of product cost, the time delay of investment income, and so on.

• ·对所建立的改进收益现值模型中一些参数的合理确定进行了深入的研究，主要包括油气产量预测方法的选择、油气价格的确定、成本费用及税金的计算、投资的确定和折现率的选择。